1. Technical Field
The disclosure generally relates to a method for depositing germanium compound materials on a substrate. In particular, the disclosure relates to electrodepositing germanium compound materials, which may include germanium-antimony-telluride (GeSbTe) as a phase change material, on an exposed region of a substrate structure. The disclosure further relates to a semiconductor or phase change device having electrodeposited germanium compound materials formed on an exposed surface thereof.
2. Discussion of the Background
Phase change (PC) materials have a wide variety of applications in microelectronic devices, such as optical storage media and solid state phase change memory. PC materials generally refer to the materials that may be switched between two phases, amorphous and crystalline. Contrast between the two phases in optical reflectivity or electrical resistivity may be used as binary digital information in electronic logic devices. Sb based PC materials have been widely used in optical storage and phase change memory. Among them, germanium containing compounds, which may include GeSbTe, exhibits a higher phase transition temperature and improved phase stability and thus is particularly of interest for PC devices.
PC materials are currently formed by vapor deposition processes, such as sputtering and evaporation. Such processes produce a continuous PC film and needs extra processes to pattern into structures. Electrodeposition, which also may be referred to as electroplating or electrochemical deposition, is a selective deposition process and is a preferred process for forming separate metallic structures. In addition, the structures produced by electroplating process are defined by the substrate patterns, from which the structures grow, and therefore may be easily scaled down accordingly. However, the electroplating method for forming germanium compound materials is not available.
There have been some limited suggestions of electrodeposition of germanium onto metals. However, these efforts have been thwarted due to the relatively high reversible potential of Ge and the very low hydrogen overpotential on Ge surfaces. As all the plating current results in proton reduction, no Ge plating will occur once the electrode surface is covered by Ge. Therefore, either an extremely alkaline aqueous solution or an organic solvent is used in Germanium deposition to suppress the proton reduction. (See generally Fink et al., Journal of the Electrochemical Society, vol. 95, p. 80 (1948); U.S. Pat. No. 2,690,422 to Szekely and Endres; and Electrochemical and Solid State Letters, vol. 5, p. C38 (2002)).
However, these methods are not compatible for germanium compound deposition for PC devices. In the non-aqueous solution approaches, where a GeCl4 solution in glycol and ionic liquid is generally used, Sb and Te salts cannot be readily dissolved and co-deposited. The techniques also suffer from the disadvantages of high viscosity and expenses. In the alkaline aqueous solution approach, the extremely high pH causes damages to most of the device structures that are built from dielectrics such as silicon oxides.
A co-pending patent application, U.S. patent application Ser. No. 11/774,105, entitled “Method of Making Phase Change Materials By Electrochemical Atomic Layer Deposition” and incorporated herein by reference in its entirety, generally discloses an atomic layer electrochemical deposition method to form single crystalline phase change materials. In particular, in the method of the application, each element is electrochemically deposited in a layer-by-layer fashion from separate solutions. In addition, an apparatus and a preprogrammed plating scheme are applied repeatedly, producing a single crystalline deposit. In the present patent application, a method is disclosed to electrochemically deposit germanium compound materials from a single aqueous solution containing all the elements.